The present invention relates generally to the detection of extravasation of fluids injected into the vascular system, and, more particularly, to extravasation detection devices and methods in medical injection procedures using electrical energy transmission through tissue in the vicinity of an injection site or other site.
In many medical diagnostic and therapeutic procedures, a physician or other person injects a patient with a fluid. In recent years, a number of injector-actuated syringes and powered injectors for pressurized injection of contrast medium in procedures such as angiography, computed tomography, ultrasound and NMR/MRI have been developed.
Extravasation is the accidental infusion of an injection fluid such as a contrast medium into tissue surrounding a blood vessel rather than into the blood vessel itself. Extravasation can be caused, for example, by fragile vasculature, valve disease, inappropriate needle placement, or patient movement resulting in the infusing needle being pulled from the intended vessel or causing the needle to be pushed through the wall of the vessel. Furthermore, high injection pressures and/or rates of some modern procedures increase the risk of extravasation. In computed tomography, for example, contrast injection flow rates can be in the range of 0.1 to 10 ml/s.
Moreover, extravasation can cause serious injury to patients. In that regard, certain injection fluids such as contrast media or chemotherapy drugs can be toxic to tissue if not diluted by blood flow. It is, therefore, very important when performing fluid injections to detect extravasation as soon as possible and discontinue the injection upon detection.
Several extravasation techniques are known in the art. Two simple and very useful techniques for detecting extravasation are palpation of the patient in the vicinity of the injection site and simple visual observation of the vicinity of the injection site by a trained health care provider. In the palpation technique, the health care provider manually senses swelling of tissue near the injection resulting from extravasation. By visual observation, it is also sometimes possible to observe directly any swelling of the skin in the vicinity of an injection site resulting from extravasation.
In addition to palpation and observation, there are a number of automatic methods of detecting extravasation that include automatically triggering an alarm condition upon detection. For example, U.S. Pat. No. 4,647,281 discloses subcutaneous temperature sensing of extravasation to trigger such an alarm. In this method of extravasation detection, an antenna and a microwave radiometer instantaneously measure the temperature of the subcutaneous tissue at the site where fluid is injected. An algorithm periodically determines the temperature difference between tissue and injected fluid, and compares the difference to a fixed threshold. An alarm processor uses the comparison to determine an alarm condition.
In addition, U.S. Pat. No. 5,334,141 discloses a microwave extravasation detection system employing a reusable microwave antenna and a disposable attachment element for releasably securing the microwave antenna to a patient""s skin over an injection site. The attachment element holds the antenna in intimate contact with the patient""s skin to optimize microwave transfer therebetween, while shielding the antenna from environmental noise signals.
Several plethysmographic detection techniques are available in addition to known temperature sensing techniques. For example, mercury strain gauge plethysmographs measure the volume change resulting from venous blood flow in a cross sectional area of a limb of a patient. Air cuff or pulse volume recorder plethysmographs measure the changes in pressure within a recording cuff caused by the change in volume of a limb or digit as a result of extravasation. Photo-plethysmographs measure the optical scattering properties of capillary blood to detect the presence of extravasated fluids in tissue. An example of a photo-plethysmograph is described in U.S. Pat. No. 4,877,034.
Impedance plethysmographs measure changes in the electrical impedance in a defined tissue volume of a limb. In this method, an impedance change of a certain level in the vicinity of the injection site is interpreted as being an extravasation. A change in impedance occurs during extravasation because injection fluid in the tissue of the patient changes both the volume and the electrical impedance properties of the tissue. An example of an impedance measurement device for sensing extravasation of radiographic contract medium is the EDA(trademark) patch manufactured by E-Z-EM, Co. of Westbury, N.Y. Maintaining suitable electrical contact between the electrodes of similar impedance plethysmographs and the skin of the patient, however, is often very difficult in such impedance measuring devices.
Although the EDA patch is capable of providing extravasation detection at speeds required by high injection-rate procedures when good electrical contact is maintained, the placement of the patch over the injection site prevents simultaneous performance of unobstructed palpation and visual examination by the health care provider. Other automatic methods for detecting extravasation also result in obstruction of the injection site and prevent palpation and visual observation. In the case of the photo-plethysmograph, for example, it is also critical to make direct contact with the skin to sense small changes in light scattering from the superficial layers of tissue. Unfortunately, preventing palpation and visual observation eliminates a valuable warning of the occurrence of extravasation.
It is, therefore, very desirable to develop improved devices and methods for detecting extravasation during the high flow rate procedures (1 to 10 ml/sec) typically encountered in angiographic, CT, ultrasound, and MR imaging procedures.
The present invention provides generally a device and method for the detection of extravasation in an injection procedure including at least a first energy source for supplying energy to tissue in the vicinity of a site and at least a first receiver to measure a signal resulting from changes in the energy supplied to the tissue by the first energy source. The signal will change when extravasation occurs due to a change in the bulk electrical properties of tissue and injected fluid in the region of the extravasation. Unlike prior devices for the detection of extravasation, the first energy source and the first receiver are positioned in a manner so that the vicinity of an injection site or other site is available for manual palpation and is visible for visual inspection.
In several embodiments, the energy source and the receiver contact the skin of a patient. In one embodiment, the device includes a base (for example, a patch) incorporating a sensor or transducer including the first energy source and the first receiver. Such a base or patch preferably has an open portion so that the vicinity of a site is available for palpation and is visible for visual inspection. Alternatively, the first energy source may be incorporated in a first base or patch and the first receiver may be incorporated in a second base or patch so that the vicinity of the site is unobstructed.
The device of the present invention preferably includes at least a second energy source to supply energy to tissue in the vicinity of the site, and at least a second receiver to measure a second signal resulting from the energy supplied to the tissue by the second energy source. The multiple energy source/receiver pairs of the present invention can be incorporated in a single or multiple bases or patches as described above. The energy source/receiver pairs are preferably oriented differently with respect to the tissue in the vicinity of the site.
In another embodiment of the present invention, the first energy source and the first receiver do not contact the skin of a patient and, therefore, keep the vicinity of the site available for palpation and visible for visual inspection. For example, the first energy source may include a source of radio frequency energy and the first receiver may include a coil. In this embodiment, the device measures inductive impedance of a region of the tissue. The first receiver may also include two coils so that the device measures the inductive coupling of the two coils.
The present invention also provides a device for the detection of extravasation in an injection procedure including a first energy source to supply energy to tissue in the vicinity of an injection site or in the vicinity of another site remote from the injection site and a first receiver to measure a first signal resulting from the energy supplied to the tissue by the first energy source. The device further includes at least a second energy source to supply energy to tissue in the vicinity of the site and at least a second receiver to measure a second signal resulting from the energy supplied to the tissue by the second energy source. The first energy source and first receiver pairing are orientated differently with respect to the site from the second energy source and second receiver pairing. In this manner, measurements across different orientations of the tissue in the vicinity of the site can be maintained. Preferably, the first energy source and first receiver pairing is oriented generally orthogonal to the second energy source and second receiver pairing.
The present invention also provides a device for the detection of extravasation in an injection procedure including a first layer of a material with relatively high dielectric constant. Preferably, the first layer of material has a dielectric constant of at least approximately 5. An example of a suitable material for the first layer is vinylidene fluoride film (for example, Kynar(trademark) available from Elf Atochem), having a dielectric constant of approximately 7. The device also includes a second layer of a relatively low dielectric material. Preferably, the material of the second layer has a dielectric constant of less than approximately 4. An example of a suitable material for the second layer is a polyimide film (for example, Kapton(trademark), available from Dupont, Inc.), having a dielectric constant of approximately 3.5. The device further includes at least one energy source/receiver pairing as described above. The energy source and the receiver are positioned between the first layer and the second layer. The second layer is positioned outside of the first layer relative to the tissue. A layer of a hydrogel material may be positioned between the first layer and the tissue to improve electrical coupling.
The device may further include a third layer of a conductive material such as a thin film of indium-tin oxide. The third layer is positioned outside of the second layer relative to the tissue and is of sufficient conductivity to shield the device from stray capacitance which can drain electrical energy from the exposed combination of electrodes and tissue, thereby reducing the sensitivity of measurement.
The present invention still further provides a device for the detection of extravasation in an injection procedure including an energy source/receiver pairing as described above and a layer of a conductive material to shield the device from stray capacitance.
In some patients, extravasation sometimes occurs at a site remote from the catheter insertion point (that is, the injection site). The present invention thus also provides a method for detecting extravasation in an injection procedure comprising the step of positioning at least a first sensor adapted to detect extravasation at a position or site remote from an injection site, but along a path of potential extravasation. A second sensor adapted to detect extravasation is preferably also positioned in a vicinity of the injection site.
The present invention also provides a system for the detection of extravasation in an injection procedure including a first sensor positioned to detect extravasation in the vicinity of an injection site and at least a second sensor positioned to detect extravasation at a site remote from the injection site. An array of such sensors or transducers can be provided along a path of potential extravasation.
Such sensors can be formed as described above. For example, the first sensor may include at least a first energy source to supply energy to tissue in the vicinity of a site and at least a first receiver for measuring a signal resulting from the energy supplied to the tissue by the first energy source. The first energy source and the first receiver are preferably positioned in a manner so that the vicinity of the site is available for palpation and is visible for visual inspection.
The present invention also provides a method of detecting extravasation in an injection procedure including the steps of: positioning a first energy source and a first receiver in a manner so that the vicinity of a site is available for palpation and visible for visual inspection, applying energy to tissue in the vicinity of the site via the first energy source, and measuring a signal resulting from the energy supplied to the tissue by the first energy source with the first receiver.
The present invention further provides a method for detecting extravasation in an injection procedure comprising the steps of: positioning a first sensor in a first orientation relative to a site, positioning at least a second sensor in a second orientation, different from the first orientation, relative to the site. As described above, the first sensor may include a first energy source to supply energy to tissue in the vicinity of the site and a first receiver to measure a first signal resulting from the energy supplied to the tissue by the first energy source. Likewise, the second sensor may include a second energy source to supply energy to tissue in the vicinity of the site and a second receiver to measure a second signal resulting from the energy supplied Lo the tissue by the second energy source.
The present invention also provides a method for detecting extravasation in an injection procedure performed on a patient including the steps of: positioning an energy source and a receiver between a first layer of a high dielectric material and a second layer of a low dielectric material, the second layer being positioned outside of the first layer relative to the patient, supplying energy to tissue in the vicinity of an injection site via the energy source, and measuring a resulting signal with the receiver.
Still further, the present invention provides a method for detecting extravasation in an injection procedure comprising the steps of: supplying energy to tissue in the vicinity of an injection site via an energy source, measuring a resulting signal with a receiver, and shielding the energy source and the receiver from stray capacitance with a conductive material.
The present invention and its attendant advantages will be further understood by reference to the following detailed description and the accompanying drawings.